1. Field of the Invention
This invention relates to grinding machines of the type in which a support for holding a workpiece to be ground by a driven grinding wheel is mounted for rotation about its axis, for example during form grinding.
2. Brief Description of the Prior Art
When using a form grinding machine, it is important to ensure that the torque loading between the grinding wheel and the workpiece does not become too high. Too high a torque loading can cause damage or excessive wear to the grinding wheel, and/or a bad surface finish on the ground workpiece.
To control the torque loading, it has previously been known to limit the rate of feed of the grinding wheel into the workpiece. Thus, in so-called "creep-feed" grinding machines the grinding wheel is hydraulically fed into the workpiece at a very low rate and the control circuit for the hydraulic feed includes a dump valve to limit or stop the feed if the torque loading between the grinding wheel and the workpiece becomes excessive.
However, a stage will generally be reached at which the grinding wheel has been fed into the workpiece by the required maximum amount, but grinding must continue while the workpiece is rotated until it has been ground to the desired depth about its entire periphery. The creep feed control will have no effect on the torque loading during this period.
Previously control on the torque loading has been controlled by empirically determining a suitable rate of rotation of the workpiece support whether by an electric motor or by hand. However this cannot accurately take into account variations in the radial extent of the workpiece, the depth that the grinding wheel is into the workpiece, the shape that is being ground, irregularities in the workpiece, and certain other factors which affect the torque loading. Under manual operation, these can partially be accommodated, but much will depend on operator skill and moreover it is desirable to be able to carry out a completely automatic grinding operation.